Thursday, March 10, 2011

Gluten-Free January Survey Data, Part I: Demographics and Limitations

Thanks to Matt Lentzner for organizing Gluten-Free January, and everyone who participated and completed the survey, we have a nice data set illustrating what happens when a group of people stop eating gluten for a month. Janine Jagger, Matt and I have been busy analyzing the data, and I'm ready to begin sharing our findings.

GFJ had over 500 participants, 527 of which received the survey and 279 of which completed the survey at the end of the month. Of those who received the survey, 53 percent completed it. I think these are respectable numbers for a survey of this nature, and it reflects the conscientious nature of the people who participated in GFJ.

Demographics

Although respondents were primarily from the United States, I'm happy to say that the data represent 18 different nationalities:

Respondents represented a diversity of ages, the largest group being 30-39 years old, with similar numbers in the 20-29 and 40-49 year groups.Respondents were just under 2/3 women.

Respondents represented a variety of weights, but the sample was biased toward lean people, in comparison with the general population. There were not many obese participants.Overall, I was pleased to see that the demographics were quite diverse, particularly in the age and gender categories.

Limitations

There are a few caveats to keep in mind when interpreting the survey results:

GFJ participants do not represent a random cross-section of the population at large. They represent primarily health-conscious individuals who were motivated enough to make a substantial dietary change. In addition, many of the people who participated probably did so because they already suspected they had a problem with gluten.

The survey response rate was 53%. Although I think that's a reasonable number considering the circumstances, it leaves open the possibility that survey responders differ from non-responders. It's conceivable that participants with better adherence and better outcomes were more likely to complete the survey than those who did not adhere to the diet or had neutral or unfavorable outcomes, despite our efforts to encourage everyone to complete the survey regardless of adherence or outcome. So the results could be biased toward positive outcomes, meaning that we will need to see a strong effect for it to be believable.

This was a non-blinded diet trial without a control group. There's no way to know how much of the effect was due to avoiding gluten per se, how much was due to overall changes in diet patterns, and how much was a placebo effect.

With that in mind, what can we take from the survey data? I feel that we can use it to answer the following question: "what is likely to happen when a motivated, health-conscious person decides to avoid gluten for a month?" And I think we can also use it to generate (but not test) hypotheses about the effects of eating gluten on the general population.

10 comments:

i find it interesting that 80% or more of the participants consider themselves from a bit underweight up to 19 pounds overweight. i wonder why there weren't more overwieght participants? are they less likely to experiment with something like an elimination diet?

Chuck: I would say - belonging, as I do to the slightly more than 19 lbs overweight demographic - that that group is actually far more inclined to try anything: desperation is a high motivator. I did offer (coming late to the party) to complete a survey, since I did effectively go gluten free in January, but was turned down by the powers that be. As it happens, my prediction that survey participants would likely self-select for success seems to have been borne out by the results. If you're interested, I derived no benefit whatsoever from gluten-freeness. Like a lot of people who struggle life-long with weight, and who tend to be highly cynical about gimmicks like this one (having tried just about all of them at one point or another) the overweight are far MORE likely to experiment with elimination diets than you slender hearty-parties who have no need for diets beyond curing the occasional blemish or stomach ache. We just don't get any good out of the process, and get mocked for it in the bargain, thank you.

There key issue is nationality and orgin to me. We know those who descend from the fertile crescent are better adapted to grains than Eurasians. That is an obvious confounder. None the less I like the informal data and we should study it so see what we can garner. I have most my patients avoid all grains anyway so I think it helps. Those from the middle east seems to be well adapted to grains.

Simoons suggested that gluten (wheat, barley and rye) consumption exerted a negative selective pressure on haplotypes predisposing to celiac disease (CD), which would explain why high frequencies of genes that predispose to CD occur in European populations with the least evolutionary exposure to cereal grains.

And this theory was accepted by most researchers, until CD specialist, Dr. Carlo Catassi, presented data challenging it.

It seems the overall prevalence of CD does not show a decreasing trend from European to Middle Eastern countries. Furthermore, as observed by Catassi, the DQ2 genotype, which is found in almost 90% of celiacs, is more common in Turkey than in the UK. On the contrary, the HLA-DR3 gene (in linkage disequilibrium with DQ2) is more common where wheat is a staple food, and rare or absent in populations traditionally consuming non-gluten foods. According to Catassi, this can be explained because the enteropathy derived from gluten intake (which was supposedly milder in early Neolithic farmers, in part due to prolonged breastfeeding and timing of gluten ingestion) may have conferred some protection against intestinal infections, therefore leading to the positive selection of CD predisposing genes.

Se:

http://www.ncbi.nlm.nih.gov/pubmed/20560212

http://www.ncbi.nlm.nih.gov/pubmed/18664863

http://www.ncbi.nlm.nih.gov/pubmed/15735480

http://www.ncbi.nlm.nih.gov/pubmed/15506671

We should not forget that sometimes genes important for early reproductive survival can be selected despite potential harm in old age. Other examples are hemochromatosis and various hemoglobinopathies that confer protection against malaria.

Furthermore, Celiac Disease depends not only on genetic predisposition and gluten intake, but also reduced breastfeeding time coupled with early introduction of gluten, certain infections, microbiota imbalances, Vit D deficiency (vitamin D appears to have a protective role regarding autoimmunity).

Finally, I remember reading a paper I can't find again saying that today's wheat has more gluten than ancient wheat.

Having said, gluten sensitivity exists and is not the same as CD.

http://www.ncbi.nlm.nih.gov/pubmed/19940509

And gluten ataxia and the role of gluten in autoimmune diseases and schizofrenia doesn't necessarily depend on CD.

I suspect under-reporting of weight played a role, as well as the group being leaner than the population at large.

Hi Megaera,

The "powers that be" did not let you take the survey because it was closed to everyone by the time you asked, as I explained to you. I know people with serious conditions who would disagree with your flippant characterization of gluten sensitivity.

Hi Pedro,

Thanks. I think it's really interesting the different way in which agricultural populations have adapted genetically. Some ofthe adaptations seem pretty crude in the sense that they have nasty side effects.

They show that if you stop eating "bread, muffins, pasta, biscuits, cookies .... " etc, your health will in most cases be better.

How this connects to gluten is beyond me, gluthen being only 1 chemical there.

Its much more probable, IMO, that improved conditions are due to the low carb diet tendency.

Lets see how LC helps - Immunity Should be better, as sugars block Vitamin C as of GLUT competition which dampens phagocitic index of WBC substantially which leads to more infections with more symptoms. Aside, Vitamin C attenuates adaptive immune system which is responsible (at least in part) for autoimmune diseases. Sugars also glicate proteins, immune system must degrade them, loosing valuable resources and leading to more production of proteins to replace the missing ones which means that cell doesn't do other things it has to do.

- BloatingCH problem. Avoid CH and bloating is mostly gone.

- Transit Problems Mixing CH with proteins, which is what people typically do, slows down transit. Its one of the principles of food combining. CH is digested in alkaline environment while proteins in acidic. Together, digestion is slowed down for both. Also, food rottens and might cause immunity problems again. On the other hand, less CH means less fiber, so that's negative factor. I suppose that most people compensated missing CHs with fruits, so fiber levels were probably similar in both diets.

- Weight Change CH influence insulin levels. Low level of CH specialize cells for digestion of fats and proteins and also lead to lower levels of insulin which promotes lipolisis -> loosing weight in overweight people and less noticeable effect for other people

- Acid reflux CH alkalize the stomach which translates to less acidic environment which might lead to H. Pylori and other infections.

About Me

I'm a writer and science consultant with a background in neuroscience and obesity research. I have a BS in biochemistry and a PhD in neurobiology. I'm the author of "The Hungry Brain: Outsmarting the Instincts That Make Us Overeat".

Copyright 2008-2017

Please feel free to reproduce the contents of this blog, on the condition that you:

1) Attribute the work to me

2) Provide a link to the page where you found it

3) Do not use it for commercial purposes

Financial disclosure

I am a co-creator of the Ideal Weight Program, and I receive revenue from the sale of this program.

In addition, I am registered as an Amazon affiliate. I may receive a small commission on the sale of some of the books I review, or other products sold through Amazon.

Disclaimer

This blog is a compilation of my opinions. It's not advice; it's information that you can take or leave as you please. I don't intend it to replace professional medical consultation or treatment. Your health is in your own hands.